Cause analysis and solution of spark discharge cau

Cause analysis and solutions of spark discharge in electrostatic precipitator

through the cause analysis of spark discharge or frequent flashover in the cold charged field boost and normal operation of electrostatic precipitator electric field, the possible parts of spark generation are eliminated item by item, and the possible causes are judged according to the actual operating conditions of electrostatic precipitator and the changes of electric field operating parameters, and the optimization, improvement, and Regular inspection, key precautions and other solutions and preventive measures to reduce the probability of spark discharge in the electrostatic precipitator electric field and ensure the reliable, stable and efficient operation of electrostatic precipitator for a long time

preface

with the continuous deepening of the transformation of ultra-low emission of flue gas in thermal power plants, the requirements for hourly average data of flue gas emission are becoming more and more strict, which requires that environmental protection facilities must be in 100% reliable operation state, so the operation stability of electrostatic precipitator electric field is very important for ultra-low emission of dust. However, the stable operation of the electric field is seriously disturbed when spark discharge is generated in the electric field of electrostatic precipitator, and even the electric field backup occurs, resulting in the reduction of the efficiency of electrostatic precipitator. Therefore, it is necessary to analyze the causes of spark discharge or frequent flashover in the cold charged field boost and normal operation of the electrostatic precipitator electric field, eliminate the possible parts of spark one by one, judge the possible causes according to the actual operating conditions of electrostatic precipitator and the changes of electric field operating parameters, and put forward solutions such as equipment optimization, improvement, regular inspection and key precautions for spark discharge in the electrostatic precipitator electric field, Reduce the probability of spark discharge in the electrostatic precipitator electric field and ensure the reliable, stable and efficient operation of electrostatic precipitator for a long time

1 principle and phenomenon of spark discharge

electrostatic precipitator is a dust removal device that uses DC negative high voltage to ionize the gas, produce corona discharge, and then charge the dust. Under the action of strong electric field force, the dust is separated from the gas. DC negative high voltage is separated from the cabinet through high voltage and connected to the cathode system. The cathode system is suspended in the middle of the anode plate by the hanging device. Porcelain bottles are used between the hanging device and the supporting steel beam Insulation board for insulation. The cathode rapping is fixed on the cathode frame and also has high-voltage DC negative current, which is insulated from the external transmission device, ceramic shaft and insulating plate. The anode is directly suspended on the precipitation beam connected to the dust collector body and reliably grounded with the dust collector shell. Spark discharge is different from corona discharge. In the process of putting the electric field into operation, when the high voltage is introduced and the high voltage direct current reaches a certain voltage dividing point, the electrostatic precipitator cathode will instantly produce sparks, and the gap between the cathode and anode will break down, accompanied by loud discharge sound and sparks splashing. In serious cases, it is equivalent to the connection of the cathode and anode, causing the anode plate to burn through. It can be seen from the control picture of the upper computer of the electrostatic precipitator that the secondary voltage and secondary current drop instantaneously, the surface meter swings frequently, and the cremation rate displays figures. The general spark discharge will limit the voltage and current parameters to a certain range, and if it is serious, it will directly cause the electric field backup

2 cause analysis of sparks

2.1 factors in flue gas and dust characteristics

electrostatic precipitator is designed and installed according to the combustion coal and boiler operating conditions, and specifies its applicable coal (including sulfur content, moisture, ash, etc.), boiler exhaust temperature, flue gas volume, humidity, dust content and dust characteristics, etc. when the boiler combustion coal changes and the actual operating conditions of the boiler deviate greatly from the design parameters, The operation of electrostatic precipitator will not adapt, and electric field spark discharge is easy to occur. The nature of flue gas mainly depends on the composition of coal, as well as the combustion mode of boiler, the type of pulverizing system and its operating conditions. The properties of dust mainly depend on the chemical composition, phase structure, physical and chemical characteristics, dust concentration, specific resistance, particle size distribution, shape, size, density, adhesion, etc. The flue gas discharged after combustion contains certain moisture, which is beneficial to the operation of electrostatic precipitators and the establishment of more factories in the future. Generally, if there is much moisture in the flue gas, the dust removal efficiency is high. If the moisture in the flue gas is too large, although it will not have an adverse impact on the performance of the electrostatic precipitator, a large amount of water vapor will be deposited on the dust collector plate with the charge of the dust. Due to the large moisture content, the adhesion of the dust will change, and it will become more and more difficult to vibrate and clean up, making the ash deposition thicker and thicker, the heteropolar distance smaller, generating spark discharge, and the ash layer will be partially ionized, which will seriously affect the normal operation of the electric field

2.2 factors of electrostatic precipitator body

(1) the deformation spacing of electrode plate and polar line becomes smaller, and discharge occurs: during operation, when the ash hopper is full of ash and cannot be discharged in time, the expansion of anode plate is blocked, the electrode plate is partially bent, and the heteropolar distance becomes smaller; When the rapping rod of the anode plate is blocked, the splint under the anode plate bends during the rapping process, resulting in the overall bending of the anode plate row and the reduction of the heteropolar distance; The connecting groove of the anode plate row is damaged, and the adjacent anode plates are not integrated with each other. Because the anode plate is long and thin, and the rigidity is insufficient, it is easy to bend, and the heteropolar distance becomes smaller; The expansion distance of cathode line is blocked, the polar line is deformed, and the heteropolar distance is reduced; The cathode wire body is not rigid enough, local bending deformation occurs, and the heteropolar distance becomes smaller; At present, there are mainly polyether ether ketone (PEEK), polyether ketone (PEK), polyether ketone ketone (PEKK), polyether ether ketone ketone (PEKK) and polyether ketone ether ketone ketone (PEKEKK); The tightening force of cathode helix decreases, relaxation and swing occur, and the local gap becomes smaller

(2) the cathode small frame is partially deformed or displaced, resulting in discharge: during operation, because the cathode small frame bears the rapping force of cathode rapping, the cathode rapping operates for a long time, resulting in local deformation of the small frame, and the distance between the anode plate and the cathode frame becomes smaller; The connecting rod of the cathode small frame is partially welded or broken, resulting in a smaller distance between the frame and the polar plate: individual cathode hanging rods sink, resulting in the overall offset of the cathode frame in a certain direction, and the overall heteropolar distance becomes smaller

(3) the limit of the anode plate is damaged or too low, and the electrode plate is discharged from the groove. During operation, the anode plate rapping rod is subjected to the rapping force of the rapping system for a long time, and the piston moves back and forth. The limit plates on both sides are worn out or welded off for a long time, and the lower part of the electrode plate row swings to both sides, sometimes there is a direct short circuit with the cathode system; When the ash hopper is full of ash, the accumulated ash reaches the electrode row, and the expansion of the electrode row is blocked. With more and more accumulated ash, the electrode row will be pushed out of the slot by the accumulated ash, resulting in spark discharge or direct short circuit

2.3 factors in power supply and control part

(1) insulator damage or serious ash deposition, creepage discharge occurs: insulating porcelain bushing and porcelain shaft are used to support and insulate the discharge system. During operation, a layer of dust and dirt is often deposited on the surface of porcelain bushing, and the insulation level is reduced. Under the action of high voltage, creepage phenomenon occurs, and breakdown discharge occurs. The long-term discharge also causes the dust-proof plate surface to carbonize, so that the electric field voltage flashover frequently and cannot operate at high voltage; The insulating porcelain bushing and insulating porcelain shaft run for a long time. At the same time, because the pressure bearing parts will crack or cut-off fracture, the insulation performance will be reduced to the minimum, and the electric field discharge will be serious

(2) insulator heater does not heat and air leakage condensation, resulting in discharge: this situation generally occurs after the maintenance of the electric field, the weather temperature is low, the insulator heater is damaged, does not heat or not heat, the insulator temperature is low, the water vapor condensation on the surface of the insulating parts, the insulation drops seriously, and discharge occurs; When the installation of manhole door, electric heater and temperature measuring device leaks, the electronic universal testing machine can solve the bottleneck problem of after-sales service. Serious wind can cause rainwater to directly invade the insulator room, and the surface of high-voltage insulator and cathode rapping porcelain shaft is polluted by water vapor to generate creepage; When the flue gas temperature is low, the temperature of insulator chamber is mainly maintained by electric heating and hot air heating, and when the flue gas temperature rises, it is mainly maintained by the heat carried by the flue gas. The size of insulator chamber has a great influence on the rise and maintenance of temperature

(3) damping resistance failure; When the damping resistance wire is partially broken or cracked, the input electric field will cause violent discharge; If the damping resistance fails or the tension drops, the electric field will discharge when it is put into operation

3 solutions to sparks in the electric field

3.1 strictly control the characteristics of flue gas and dust

in order to eliminate the impact of coal changes on the dust removal efficiency of the electrostatic precipitator, under the normal operation of the dust removal equipment system, each set of electrostatic precipitator should carry out at least one characteristic test for typical coal types to determine the comprehensive impact of coal types, power supply and rapping on the efficiency of the electrostatic precipitator and find out the best operation mode of the electrostatic precipitator. At the same time, according to the ash content of the actual combustion coal, formulate a suitable rapping cycle, and set the rapping cycle and rapping time by load section. In particular, when the electric field backup occurs in the first electric field, the rapping cycle of the second electric field should be adjusted in time, such as PVC pipes with a diameter of 1m. Because the first electric field backup, the dust collection pressure of the second electric field increases, which is equivalent to more than 85% of the ash collected by the second electric field. If the rapping cycle is still the original cycle, the ash accumulation on the anode plate cannot be cleaned in time, and serious spark discharge will occur, which not only has a poor dust collection effect, It is also prone to secondary dust, so the vibration cycle of the secondary electric field should be shortened in time. The water content of normal combustion coal will not be very large, and the size of the deviation will not affect the operation of the electric field. At present, the water content in the flue gas increases significantly mainly due to the water flushing of the air preheater. The water volume of the water flushing of the air preheater is more than 20 tons per hour. Through the high-temperature evaporation of the flue gas, the water vapor in the flue gas is many times higher than that in normal operation. The water vapor and dust in the flue gas are mixed and collected on the anode plate, which has strong adhesion and is not easy to be removed by rapping, so high-pressure water washing has seriously threatened the normal operation of electrostatic precipitator. The feasible solution is to increase the exhaust gas temperature as high as possible, and the flue gas after entering the electrostatic precipitator should be higher than the dew point temperature as much as possible to avoid the generation of condensate. At the same time, when the air preheater is washed with high-pressure water, the electric field rapping cycle should be adjusted in time, and the electric field parameters will operate the voltage and current, so as to avoid too much ash sticking on the polar line of the electrode plate and spark discharge

3.2 improve the maintenance quality and operation reliability of electrostatic precipitator

strengthen the management of maintenance quality in the maintenance of electrostatic precipitator. The cathode prick wire and spiral wire shall focus on the inspection of open welding, bending and prick bending, and shall be checked, corrected and reinforced one by one. Those with reduced strength and serious damage that cannot be repaired must be replaced during the inspection, the spacing between cathode and anode shall be adjusted, and the measurement results before and after adjustment shall be recorded; The anode plates shall be checked row by row, and the bending of the plates shall be corrected. If the vibration of the rapping rod is blocked and deformed, effective measures shall be taken to eliminate it. Air leakage will not only increase the flue gas treatment capacity of the electrostatic precipitator, but also cause condensed water due to temperature drop, resulting in ash deposition and hypertrophy of the corona wire, creepage of the insulating sleeve, and spark discharge. Mainly check the air leakage of all manhole doors of the electrostatic precipitator body and replace the packing; Replace all the packing of the electrostatic precipitator anode rapping through the wall shaft seal, and replace the packing for 3 cycles, with a 45 ° difference between each cycle; Check the air leakage at the heating magnetic sleeve of electrostatic precipitator insulator, girder heating and cathode rapping porcelain shaft in detail, and deal with the air leakage point

4 conclusion

find out all factors and equipment parts that may produce spark discharge by analyzing the causes of spark discharge or frequent flashover in the electric field, and